1. Field of the Invention
The present invention relates to an apparatus and process for rapidly filling a hydrogen tank with hydrogen while suppressing exothermic phenomenon during the course of filling.
2. Description of Related Arts
Recently, from the viewpoint of the expression of the amount of carbon dioxide exhausted, vehicles utilizing hydrogen (H2) as a fuel, such as fuel cell carried vehicle and hydrogen engine vehicle, have been focused. Such a vehicle carries a hydrogen tank, and the hydrogen having been introduced in the hydrogen tank is supplied into a fuel cell or an engine to generate a drive force.
The hydrogen tank is filled with hydrogen (pure hydrogen) at a pressure of approximately 20 Mpa. The pressure within the hydrogen tank is decreased as the hydrogen is consumed with the fuel cell, etc. If the pressure within the hydrogen tank is decreased, the residue of the hydrogen is decreased accordingly, making it impossible to supply the hydrogen into the fuel cell, etc. In such a case, the hydrogen tank is filled or refilled with fresh hydrogen. For example, the fuel cell carried vehicle or hydrogen engine vehicle stops at a so-called hydrogen station at which the tank provided within the vehicle is filled with hydrogen.
A vehicle having (compressed) natural gas carried thereon (also referred to as xe2x80x9cCNG vehiclexe2x80x9d) has been known which utilize natural gas as a fuel. A natural gas tank is filled with a natural gas, for example, by connecting a natural gas source provided on a natural gas stand to the natural gas tank, and introducing the natural gas into the natural gas tank due to the pressure difference between them.
For example, Japanese Utility Model Laid-Open Publication No. 4-64699 discloses xe2x80x9can apparatus for supplying compressed natural gas into a vehicle utilizing the compressed natural gas as a fuelxe2x80x9d, in which a high pressure accumulator (which utilizes a later filling stage) and a pressure-variable accumulator (which utilizes a former filling stage) are switched to be used. This makes it possible to maintain the pressure of the natural gas source at a high temperature and then to repeatedly fill the natural gas cylinder with the natural gas in a rapid manner.
In the case where the natural gas tank (fuel cylinder) is filled with the natural gas, an endothermic phenomenon due to the Joule-Thomson effect and exothermic phenomenon due to the adiabatic compression take place at the same time and thus, the heat caused is almost offset, the temperature of the natural gas being somewhat decreased. Consequently, there is no problem associated with the heat generation when the natural gas is incorporated.
However, differing from the natural gas, hydrogen has an inversion temperature in the Joule-Thomson effect of 202 K (approximately xe2x88x9271xc2x0 C.), which is lower than the normal temperature and, thus, once the compressed hydrogen having a temperature of about normal temperature expands, the heat is generated to increase the temperature of hydrogen. Consequently, when a hydrogen tank is filled with hydrogen, the temperature of hydrogen introduced and the temperature of the hydrogen tank itself become higher, due to (a) heating-up caused by diabolically increasing the pressure within the hydrogen tank and due to (b) heating-up caused by subjecting hydrogen to expand from the hydrogen source, which has a pressure higher than that of the hydrogen tank, into the hydrogen tank (in which case, an amount of heat generated is considerably lower as in case of the diabolic compression). Specifically, unlike the natural gas, no cooling effect takes place in the case of filling with hydrogen even by subjecting hydrogen to expand into the hydrogen tank and, therefore, the temperature of hydrogen filled and the temperature of the hydrogen tank itself become unduly higher. Increasing the temperature of hydrogen filled and the temperature of the hydrogen tank itself is disadvantageous in terms of causing failure or deterioration of fittings such as PRD (pressure-relief device) and a tank liner, provided on the hydrogen tank and decreasing filling efficiency. When the hydrogen tank is made up of a fiber-reinforced plastic (C-FRP or G-FRP) in order to reduce the weight of the hydrogen tank for the purpose of improving the fuel efficiency, the heat accelerates the deterioration of the plastic. Consequently, there is an object to fill the hydrogen tank with hydrogen while suppressing the increase in the temperature of the hydrogen tank.
Also, it is important for attaining easy operability of the fuel cell carried vehicle, etc. to rapidly fill the hydrogen tank with hydrogen by increasing a filling rate of hydrogen. There is an object to rapidly fill the hydrogen tank with hydrogen without any deceleration of the hydrogen-filling rate.
The main object of the present invention is to provide an apparatus and process for filling with hydrogen, which solve the above object.
We have conducted serious studies in light of the above object, As a result, we have accomplished the present invention on the basis of the fact that the temperature of hydrogen within the hydrogen tank arrives at the maximum level in the considerable earlier stage immediately after the initiation of filling with hydrogen, and it levels off or is decreased thereafter, i.e., the temperature of hydrogen within the hydrogen tank (the temperature of the hydrogen tank) being decided at the earliest stage, etc.
According to the first aspect of the present invention there is provided an apparatus for rapidly filling a hydrogen tank with a hydrogen gas comprising:
a hydrogen source;
a hydrogen tank;
a passage which connects said hydrogen source and said hydrogen tank; and
a mechanism for varying a hydrogen-filling rate;
said mechanism for varying a hydrogen-filling rate changing the hydrogen-filling rate depending upon the pressure within said hydrogen tank.
When the hydrogen filling rate is increased, the amount of heat generated becomes higher accordingly, which increases the range of increasing the temperature within the hydrogen tank. Conversely, if the hydrogen filling rate is decreased, the amount of heat generated becomes lower accordingly, which decreases the range of increasing the temperature within the hydrogen tank. When the pressure within the tank is increased with the progress of the filling the hydrogen tank with hydrogen, the heat generation due to the adiabatic compression is decreased.
In the apparatus according to the present invention, the tank is filled with hydrogen at a decreased filling rate at the initial filling stage where a large amount of heat is generated, and a filling rate is increased as an amount of heat is decreased. By such a configuration, the heat generation at the initial filling stage where the temperature is easily increased can be suppressed. Also, since a filling rate is increased depending upon the pressure within the tank, even if it takes longer time for increasing the pressure within the hydrogen tank at the initial filling state, the delayed time can be caught up and, the apparatus and the process of the present invention can totally attain a rapidly filling with hydrogen.
In the apparatus of the present invention, said mechanism preferably has a function of introducing the hydrogen gas into the hydrogen tank at a high filling rate when the pressure within said hydrogen tank is increased.
Also, in the apparatus according to the present invention, said mechanism for varying a hydrogen-filling rate preferably comprises a filling rate variable valve having a function of changing the hydrogen filling rate depending on the pressure within the hydrogen tank at the time of hydrogen-filling.
In the apparatus where the mechanism has a function of introducing the hydrogen gas into the hydrogen tank at a high filling rate when the pressure within said hydrogen tank is increased, the mechanism for varying a hydrogen-filling rate preferably comprises a filling rate variable valve having a function of changing the hydrogen filling rate depending on the pressure within the hydrogen tank at the time of hydrogen-filling.
In the preferred embodiment of the apparatus according to the present invention just mentioned, the valve preferably possesses a valve element which is movable depending upon the pressure within the hydrogen tank to allow the hydrogen to be introduced for flowing through a passage formed between said valve element and said valve seat, and wherein said passage is widened to increase the hydrogen-filling rate, when the pressure within the tank is increased. In this apparatus, it is desired that at least one of said valve element and said valve seat possesses at least one orifice so that even if said passage formed between said valve element and said valve seat is closed due to a low pressure within the hydrogen tank, the hydrogen tank is filled with hydrogen through said orifice.
Also, in the apparatus, the valve element is moved by a pushing member such as a spring
According to this configuration, since the hydrogen is incorporated into the hydrogen tank while restricting the flow amount by the contract means, the increase in the temperature within the hydrogen tank can be suppressed. When the increase in the temperature within the hydrogen tank is suppressed, the filling efficiency can be enhanced, making it possible to fill the hydrogen tank with hydrogen in a rapid manner.
In another preferred embodiment of the apparatus according to the present invention, the mechanism preferably comprises a valve, a sensor which detects the pressure within the hydrogen tank, and a controller which controls said valve to vary the hydrogen-filling rate depending upon the pressure detected by said sensor.
In the apparatus just mentioned, it is preferred that said controller controls the valve such a manner that the hydrogen gas is introduced into said hydrogen tank at a first hydrogen-filling rate when the pressure within the hydrogen tank is lower than a predetermined pressure, while the hydrogen gas is introduced into said hydrogen tank at a second hydrogen-filling rate which is higher than said first hydrogen filling rate when the pressure within the hydrogen tank is not lower than the predetermined pressure.
Also it is preferred that said valve used varies the hydrogen-filling rate via a stepping motor.
According to this configuration, the hydrogen passage becomes wider or narrower depending upon the inner pressure within the hydrogen tank. Specifically, the passage becomes narrower as the inner pressure is decreased, and the passage becomes wider as the inner pressure is increased. Consequently, a filling rate is restricted at the initial filling stage, and the restriction is gradually released as the filling stage progresses, i.e., the inner pressure is increased with the progress of the stage.
According to the present invention, there is also provided a process for rapidly filling a hydrogen tank with a hydrogen gas from a hydrogen source by connecting said hydrogen tank with said hydrogen source comprising: initiating the introduction of hydrogen from said hydrogen source into said hydrogen tank; and varying the hydrogen-filling rate depending upon the pressure within said hydrogen tank.
In the process according to the present invention, the hydrogen filling rate is preferably changed when the pressure within said hydrogen tank is increased.
When the hydrogen filling rate is increased, the amount of heat generated becomes higher accordingly, which increases the range of increasing the temperature within the hydrogen tank. Conversely, if the hydrogen filling rate is decreased, the amount of heat generated becomes lower accordingly, which decreases the range of increasing the temperature within the hydrogen tank. When the pressure within the tank is increased with the progress of the filling the hydrogen tank with hydrogen, the heat generation due to the adiabatic compression is decreased.
In the process according to the present invention, the tank is filled with hydrogen at a decreased filling rate at the initial filling stage where a large amount of heat is generated, and a filling rate is increased as an amount of heat is decreased. By such a configuration, the heat generation at the initial filling stage where the temperature is easily increased can be suppressed. Also, since a filling rate is increased depending upon the pressure within the tank, even if it takes longer time for increasing the pressure within the hydrogen tank at the initial filling state, the delayed time can be caught up and, the apparatus and the process of the present invention can totally attain a rapidly filling with hydrogen.